Vacuum may be used to operate or to assist in the operation of various devices of a vehicle. For example, vacuum may be used to assist a driver applying vehicle brakes, turbocharger operation, fuel vapor purging, heating and ventilation system actuation, and driveline component actuation. Vacuum may be sometimes obtained from an engine intake manifold in normally aspirated engines because the intake manifold pressure is often at a pressure lower than atmospheric pressure. However, in boosted engines where intake manifold pressures are often at pressures greater than atmospheric pressure, intake manifold vacuum may replaced or augmented with vacuum from an ejector. By passing pressurized air though the ejector, a low pressure region may be created within the ejector so that air can be drawn from a vacuum reservoir to the ejector, thereby reducing pressure within the vacuum reservoir. Nevertheless, ejector systems may not provide a desired amount of vacuum or may operate less efficiently than is desired since ejectors have fixed dimensions that may be selected based on a limited operating range.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for providing vacuum for a vehicle, comprising: directing air from a compressor to an ejector; and adjusting a flow rate of air from the compressor in response to a rate of vacuum consumption within a vacuum system.
By adjusting a flow rate of air supplied from a compressor to an ejector it is possible to adjust a rate that vacuum is provided to a vacuum reservoir so that vacuum can be supplied to the reservoir at a rate that allows vacuum consumers within the vacuum system to operate as desired. Thus, the ejector may be controlled to provide vacuum at a rate that is related to the use or consumption rate of vacuum so that excess vacuum is not provided. Further, during conditions where the ejector may not have the capacity to provide a desired level of vacuum, air flow to the ejector may be deactivated and engine operation may be adjusted so that higher rates of vacuum are provided by an engine via the engine's intake manifold. In this way, it is possible to provide vacuum to a vacuum system while reducing engine fuel consumption since vacuum is provided according to vacuum use rather than simply operating the vacuum system at full vacuum supply capacity.
The present description may provide several advantages. For example, the approach may improve engine fuel economy by providing vacuum based on vacuum use rather than simply supplying a high level of vacuum. Further, the approach can prioritize vacuum use and vacuum generation according to operating conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.